1. Field of the Invention
This invention relates to a device for transporting poison rod assemblies between fuel assemblies in a nuclear fuel storage facility and, more specifically, to a device for transferring a poison rod assembly which uses an overhead crane as its only lifting mechanism.
2. Description of the Prior Art
Fuel for a nuclear reactor used to create steam and, ultimately, electricity, generally is in the form of fuel rods containing a fissile material. When fuel rods are being stored, the fuel rods are typically supported in nuclear fuel assemblies arranged as spaced parallel arrays. Fuel assemblies are stored in racks in a protective medium, such as water containing boric acid. In addition to the fuel rods, poison rods are disbursed throughout the fuel assemblies to control the fission process. Poison rods generally include a plurality of elongated rods, each containing a neutron absorbent material, which fit in longitudinal openings, or thimbles, defined in the fuel assemblies. The top end of each poison rod is attached to a web thereby forming a poison rod assembly. A T-shaped bar is affixed to the top of the web, creating an easily accessible handle for lifting the poison rod assembly so that it may be transferred from one fuel assembly to another.
As shown in Hornak et al., U.S. Pat. No. 5,325,408, prior art transfer devices use a winch located at the top of the transfer device to lift the poison rod assembly. Movement of the transfer device itself between fuel cells, is accomplished by a gantry crane in the fuel cell storage facility. Thus, prior art lifting devices consist of at least two lifting means, one to lift the transfer device itself, and one to lift the poison rod assembly within the transfer device. Lifting of a poison rod assembly could be performed more efficiently by the crane used to move the transfer device. Additionally, elimination of the winch would reduce the cost of the transfer device and eliminate unnecessary parts that are subject to mechanical failure.
Therefore, there is a need for a poison rod transfer device that does not require the use of a winch.
There is a further need for a poison rod transfer device that uses a single lifting mechanism to remove the poison rod assembly from a fuel cell and transfer it to another fuel cell.